Neutron Sciences 2008 Annual Report - 17.79 MB - Spallation ...

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58 FACILITY DEVELOPMENT 2008 ANNUAL REPORT SNS Accelerator Systems Front-End Systems All aspects of SNS front-end systems performance were improved during 2008. The ion source team (Martin Stockli, Robert Welton, Baoxi Han, Syd Murray, and Terry Pennisi) boosted the SNS baseline source so that it operates at the peak 38 milliampere (mA) current specified in the SNS design. This improvement was made possible by use of the ion source test stand, a testing platform identical ORNL NEUTRON SCIENCES neutrons.ornl.gov SNS Accelerator Systems highvoltage converter modulator. Ion Source Radio-Frequency Quadrupole to that operating on the SNS front end. By modifying the source extraction geometry, improving the management and release of cesium (used to enhance surface electron emission), and exploring the operating parameters of the source, the team was able to increase peak current to the 38-mA design level by the end of 2008. In addition, lifetime tests performed on the platform showed that a single ion source could provide reliable operation for the 16-day neutron production run cycle initiated in 2008. (For information about future plans for the ion source, see “Booster Shot for SNS Ion Source” on p. 68.) Drift-Tube Linac Front end: produces a 1-millisecondlong beam Closed-Cavity Linac The front-end systems generate the negative hydrogen ion beam, form beam particles into individual packets of charge, remove one-third of the beam by chopping, and prepare the beam for injection into the linear accelerator (linac). Superconducting Linac Superconducting Linac b = 0.61 Linac: accelerates the beam to 1000 MeV, or 1 GeV The superconducting linac uses niobium radiofrequency resonators to accelerate the beam from 186 megaelectron volts (MeV) to the final output energy. At the beginning of 2008, the linac provided
SNS accelerator complex. Superconducting Linac b = 0.81 High-Energy Beam Transport a beam energy of 860 MeV, substantially lower than the design energy of 1000 MeV, because some superconducting cavities were out of service and the superconducting resonators in the high-energy portion of the linac were operating at 15–20% below their design accelerating field. To correct these problems, repairs were completed to two cryomodules and associated superconducting cavities in the new SNS repair, maintenance, and testing facilities. The repairs will allow SNS to operate with 80 of 81 superconducting cavities, providing a linac output energy of about 930 MeV. Accumulator Ring: compresses the beam to 700 nanoseconds Ring-To-Target Beam Transport A potential superconducting cavity surface treatment process was conducted in which a radio-frequency plasma discharge was established in a superconducting cavity. The measured accelerating field after this “plasma cleaning” showed an increase of approximately 15% in cavity field, near the increase required to boost linac output energy to the design value of 1000 MeV. Next steps involve further development of this technique to enable in situ plasma cleaning of the installed superconducting cavities in the linac tunnel. FACILITY DEVELOPMENT 2008 ANNUAL REPORT Modulators The radio-frequency waves that power the linac’s accelerating cavities are generated by klystrons, which in turn are driven by high-voltage converter modulators that provide 60 pulses of 10-megawatt power per second. These are state-of-the-art pulsed power devices with advanced solid-state, high-speed, highpower switches. Since the modulator system accounts for the largest fraction of unscheduled down time, active efforts are in progress to improve its reliability. During 2008, the modulator systems were improved to allow operation at a full repetition rate of 60 pulses per second. Additional diagnostic and protection systems were built and installed to allow easier diagnosis and to protect equipment in the event of failure. A full replacement of problematic capacitors was initiated in late 2008, measurably improving reliability in the final month of 2008 operation. Contact: Stuart Henderson (shenderson@ornl.gov) Target ORNL NEUTRON SCIENCES The Next Generation of Materials Research 59 FACILITY DEVELOPMENT
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1 2008 ANNUAL REPORT Front and back
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2008 ANNUAL REPORT ORNL NEUTRON SCI
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4 INTRODUCTION 2008 ANNUAL REPORT O
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Page 90 and 91: 88 PEOPLE 2008 ANNUAL REPORT Adviso
Page 92 and 93: 90 FACTS AND FIGURES 2008 ANNUAL RE
Page 96 and 97: 94 Furnaces FACTS AND FIGURES 2008
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Page 104 and 105: 102 PUBLICATIONS 2008 ANNUAL REPORT
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108 PUBLICATIONS 2008 ANNUAL REPORT
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116 Units Acronyms and Units 2008 A
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